Spotting rifles are used to determine range to a target. In general, the spotting rifle is set for a specific range and a tracer or burning round is fired to see if the selected range was accurate. If not, corrections are made until the correct range is achieved. Frequently, a spotting rifle is coupled to another launching device. That is, the spotting rifle is used to select the range for the launching device. Accordingly, it is desirable to align the boresight of the spotting rifle with that of the launching device. The advent of the ballistically matched spotting round has greatly reduced the difficulty and time required to align the spotting round impact with the launching device's round. However, it. is still necessary to accurately align the spotting rifle barrel with the launching device.
A preferred solution to this problem is to adjust the barrel of the spotting rifle without having to relocate the entire spotting rifle in relation to the main launch tube or rifle. One such spotting rifle barrel alignment mechanism is disclosed in U.S. Pat. No. 5,657,546 in which the breech end of the spotting rifle barrel floats in a seat where it engages the spotting rifle's receiver housing. The spotting rifle barrel is clamped at its muzzle end to a bracket depending from the muzzle of the launch tube. When a spotting round is fired, inertia of the round moving towards the muzzle end of the spotting rifle barrel tends to drive the spotting rifle barrel out of its floating breech end seat in the receiver housing. Once out of its breech end seat, the spotting rifle barrel tends to lose its boresight. Further, because the muzzle end of the spotting rifle barrel is clamped to the muzzle of the launch tube, the inertia of the round causes the launch tube to bow slightly as forces generated by the movement of the spotting rifle barrel are transferred to the muzzle of the launch tube. This is especially true when the launch tube is made from a material such as fiberglass.